lecture: epididymis, ejaculation, semen

Epididymis, Ejaculation, Semen

Reading

Chapter 10
Handout on the Epididymis and Ejaculation

Spermatozoa structure

head
- acrosome
  - contains hydrolytic enzymes needed for fertilization
    - acrosin
    - hyaluronidase
- nucleus
  - highly condensed with protamines replacing histones
  - crosslinking of protamines with disulfide bonds occurs in epididymis to condense sperm DNA
- nuclear ring - formed by end of acrosome
- postnuclear cap or region
neck - joins head to tail
- implantation socket
tail
- capitulum
  - fits into implantation socket of head
- middle piece
  - first part has laminated columns
    - give neck flexability
  - axoneme
    - originates from distal centriole
    - microtubules - 9 pairs surround a core of 2 (9 + 2)
    - sliding of microtubules driven by ATPases to make sperm motile
  - coarse fibers
    - 9 coarse fibers surround the axoneme
  - mitochondria
    - surround coarse fibers
    - arranged in a helical pattern around axoneme
    - production of ATP via respiration for cell stability and motility
- annulus
  - where mitochondria terminate
- principal piece
  - composed of axoneme and associated coarse fibers
  - tough fibrous sheath surrounds the axoneme and coarse fibers
- end piece
  - portion after end of fibrous sheath and coarse fibers
Axoneme
- 2 core microtubles
- 9 outer pairs of microtubules
  - connected via radial spokes to central pair
  - nexin links connect the each of the outer pairs to each other
  - Dynein (an ATPase) located on microtuble
    - in absence of ATP dynein attached to another microtubule
    - in presence of ATP, dynein releases
    - ATP is then converted to ADP with release of energy, dynein extends, rebinds at a lower site, then dynein shortens and causes microtubules to slide past one another
    - nexin links, radial spokes, course fibers, and fiborous sheath, stretched and recoil back

Sperm metabolism

glycolysis
- most species can use glucose or fructose
- sperm hexokinase can use either glucose or fructose to make Glucose-6-phosphate or Fructose-6-phosphate respectively
- Phosphohexoisomerase converts Glucose-6-phosphate to Fructose-6-phosphate which then continues in glycolysis
- phosphatases can convert glucose-6-phosphate back to glucose in futile subtrate cycling
respiration
- not always coupled to glycolysis as in other cells
- sperm can use only glycolysis if needed
ATP utilization
- motility
- futile substrate cycling
- maintain the plasma membrane ionic gradients
- no transcription after condensation of nucleus during spermiogenesis
Temperature dependent so ATP dependent processes also temperature dependent
- sperm velocity is temperature dependent

Sperm transport in the male tract

seminiferous tubule
- fluid flow with fluid secreted by sertoli cells
- contractions of myoid cells
rete testis
- fluid flow with fluid from seminiferous tubule and secretion by rete testis cells
- some contractions of smooth muscle in mediastinum
vas efferentia
- fluid flow with fluid from seminiferous tubule and rete testis
- cilia on epithelial cells beat and move fluid along
epididymis
- muscle contractions
vas deferens
- muscle contractions
urethra
- muscle contractions

Epididymal Function

maturation
- change in fertility
- develop motility
- nuclear condensation
- cytoplasmic droplet
concentration
- remove water
secretion
- testosterone converted to dihydrotestosterone (DHT)
- energy substrates like glycerolphosphatidylcholine (GPC), free faty acids, carnitine
- glycoproteins
- lipids
- enzymes
transport
- smooth muscle contraction
storage
- cauda

Hormonal control of the epididymis

absolute requirment for androgen to function
caput
- tubal testosterone
corpus
- tubal DHT
- vascular testosterone
cauda
- tubal DHT
- vascular testosterone

Ejaculate Characteristics - Fractions

Species

Time lapse for ejaculation

Composition of Ejaculate

Bull 1 second single fraction

Ram 1 second single fraction

Boar 5-25 minutes
fractionated

sperm-free
sperm-rich
coagulum

Stallion 30-60 seconds
fractionated

sperm-free
sperm-rich
mucus

Man 10-30 seconds single fraction but coagulated

Species	Time lapse for ejaculation	Composition of Ejaculate
Bull	1 second	single fraction
Ram	1 second	single fraction
Boar	5-25 minutes	fractionated sperm-free sperm-rich coagulum
Stallion	30-60 seconds	fractionated sperm-free sperm-rich mucus
Man	10-30 seconds	single fraction but coagulated

Components of Bull Semen

water
semen
substrates
- fructose
- sorbitol
- inositol
- glycerol phosphatidyl choline (GPC)
- citric acid (not primary function)
inorganic salts (maintain osmotic pressure)
- sodium
- potassium
- calcium
- magnesium
- chloride
proteins

Initial semen evaluation

color
volume
concentration
motility
viability
morphology

Ejaculate Characteristics - specifications

Species	Ejaculate Volume (ml)	Sperm Concentration (X 10⁹/ml)	Total Sperm per Ejaculate (10⁹)	% Motile	% Normal
Bull	8.0	1.5	12	75	95
Ram	1.0	3.0	3	95	95
Boar	200	.25	50	70	90
Stallion	80	.15	12	70	40 - 90
Man	2-6	.15	.9	65	30 - 70

Impact of Heat on Spermatogenesis

Experimental technique is scrotal insulation
- in boar increased scrotal temperature by 1.9C
Requires knowledge of spermatogenesis kinetics
Pachytene Primary Spermatocyte most impacted by heat
There is a delay in impact of heat until impacted cells are ejaculated.

Review Quizzes